This invention relates to snow shovels, and more particularly to manually pushed snow shovels. Traditional snow shoveling involves lifting and throwing snow which is hard work and potentially injurious to the user's back. To reduce the work and use of the back, shovels have been developed which allow the user to physically push the snow aside rather than having to lift it. Snow is moved off of horizontal ground surfaces by sliding the push blade across the ground surface, collecting the snow on the blade and then moving the snow to a desired location and tilting or lifting the blade to remove the snow from the blade. Existing manual push shovels are not entirely adequate for the job, however, since movement through the snow can stall before an entire pass is achieved. Snow shovel stall is a consequence of the snow load compressing ahead of the blade and friction of the blade with the ground which increases in accord with the snow load increase and ground irregularity. Once stall has occurred, snow is lifted and thrown or more time is expended to slide it away on the shovel.
Certain designs in the prior art are designed to allow the user to scrape the ground in order to assure a good snow removal job. These prior art shovels have a wheel or a skid system located under the blade and behind its leading edge. Some examples of such wheel supported shovel blades are found in U.S. Pat. Nos. 1,206,235: 1,232,361; 2,460,560; 2,598,952, 2,772,490; 2,846,785; and 2,852,872. Some skid supported shovel blades are found in U.S. Pat. Nos. 2,484,409 and 5,271,169 and Canadian Patent Numbers 687,138 and 892,438.
Support behind the blade leading edge provides a fulcrum point on which the shovel user pivots the blade edge downward by the horizontally forward and the resultant upward pushing force on the handle which is the natural direction in the course of moving snow. The resultant upward motion of the handle from the pushing of the shovel horizontally forward is the result of the forward pivoting of the handle due to a friction increase against the blade. A shovel user of the prior art will have to expend energy away from the task of moving snow by fighting the shovel handle tendency to pivot forward and upward by exerting a downward counter pivoting force on the shovel handle. The prior art with the blade support behind the leading edge has this problem with blade friction with the ground and catching on irregularities in the snow.
The location of blade support behind the leading edge was apparently the logical place to carry the snow load and does somewhat reduce blade friction with the ground. However, the downward pivoting of the blade as a result of the natural forward and upward pushing force on the shovel handle results in a friction increase at the blade leading edge as the pushing on the handle is increased to overcome an increasing snow load. The increasing friction and any ground irregularities contribute to the stalling of blade forward motion. The user's natural forward and upward pushing force intensifies the stall. A downward push on the handle is required to lift the blade up and free it so the snow load can be dumped or slid out of the snow removal path.
Other shovel blades shown in U.S. Pat. Nos. 4,865,373 and 928,283 have wheels or revolving bodies in front of the blade leading edge. These relatively small wheels or bodies hold the blade leading edge close to the ground. The problem with this scheme is that during snow shoveling, the small wheels tend to get stuck in slush and surface irregularities found in gravel driveways, grass turf, brick walkways, and frozen ruts.
While small wheels can get stuck, larger wheels positioned forward of the blade may not. However, larger wheels and their mounting assembly required to hold the blade close to the ground tend to be expensive. Larger wheels resist forward motion when they freeze or rust, and by their higher profile or greater surface area against the snow.
According to this reasoning the shovel of U.S. Pat. No. 4,865,373 provides a second set of larger wheels behind and under the blade where they are less subject to breakage or failure by freezing or rusting. This also increases the blade longitudinal support and fixes the blade angle and height over and out of ground and reduces the weight shift forward to the small front wheels. So fixed and designed, the blade can build a snow load ahead of it which contributes to stalling by friction buildup or catching of the wheels.
Similar to other shovels with runners or wheels behind the blade leading edge, the specified way to relieve this friction on the U.S. Pat. No. 4,865,373 shovel is to unload the blade by moving the blade handle downward to raise the blade leading edge away from the ground. This downward movement of the shovel handle while maintaining forward shovel movement is difficult and results in snow being left behind. As stated earlier, the user natural force on the shovel handle is horizontally forward and upward and this natural force tends to intensify stalling in heavy snow.
Skids shaped with a curvature like skis or runners are found in a variety of devices more complex and elaborately constructed than a simple manual push shovel. The snow blower of U.S. Pat. No. 2,605,561 shows runners to guide a shallow angled blade over the ground. As in the prior art push snow shovels, most of the weight is balanced over the rear wheels located slightly behind the center of gravity. This precludes a forward pivot of the blade. Instead, the blade is freed traditionally by a downward handle motion that raises the blade upward while pivoting on the rear wheels.
Some automobile or truck pushed snow removal devices have had runners which carried the weight of their shovel blades directly under the blade leading edges. However, these vehicle pushed snow removal devices have fixed blade angles and fixed blade heights. The runners were actually displaced from and indirectly attached to the blades. The displaced runners of the vehicle pushed snow shovels were designed to have the flat portions of the runners maintain contact with the horizontal ground surface to be plowed. There is no pivoting on the feet or runners upon which the weight of the blades are held since the rear of the blades are affixed at a set height to a vehicle. This prohibited any rotation or pivoting of the blades on these devices. Comparison with manually pushed snow shovels is limited as a result. Some examples of vehicle pushed snow removal devices which carry the weight of the blade directly below to behind the leading edge of the blades on the flat portions of the runners are U.S. Pat. Nos. 2,884,720 and 3,391,478.
Push snow shovels of the prior art utilize skids or wheels under the blade and behind the blade leading edge. These skids or wheels support the snow load. These designs provide some improvement in the physical work required, however blade edge friction with the ground is still a problem especially over rough surfaces. The user natural forward force on the handle that causes the shovel to move forward also causes the blade edge to scrape the ground with increasing friction as the snow load builds. Eventually a stall occurs by this friction or when the blade edge or small wheels catch on a rough surface or thick wet snow.
For the foregoing reasons, there is a need for a manually pushed snow shovel with which the user's natural forward and upward pushing force on the shovel handle alleviates rather than intensifies stalling friction with the ground.